I played back in 2004-2006 mostly so maybe you all don’t understand what it did to be soft locked into your playstyle (able to respec at an increasing gold cost) if you mostly played later in the life of WoW
Yes its a penalty
Yes it feels bad to not get every optimal talent for every optimal encounter if you (and the game) is designed for min/maxing those encounters.
What did it do then that was good?
It made you decide who exactly you wanted to be and how you wanted to play and be known. If you wanted to Raid/PvP/Dungeons then you better make your spec well rounded and capable of every facet of the game. Sure you may not be “optimal” for every specific encounter, but your choice was to be good at all instead of one area.
This meant each individual was more important in whatever they valued speccing into most. Now if you were so mentally sick that you wanted to me maximum optimal in every part of the game you played in at all times then yes you could pay for the increasingly higher respec costs to switch your spec for every single thing you did.
Dual spec gives everyone more options, but makes the choices of who you play as less important in the world as every role is diluted from more roles being available.